Dilated cardiomyopathy in transgenic mice with cardiac-specific overexpression of tumor necrosis factor-alpha

The failing human heart expresses tumor necrosis factor-alpha (TNF-alpha). However, its pathophysiological significance is not clear. We previously reported that robust overexpression of TNF-alpha in the murine heart causes lethal myocarditis. In this study, we modified the transgene to reduce the production of TNF-alpha by preserving the destabilizing sequence in TNF-alpha cDNA. Expression was driven by the murine alpha-myosin heavy chain promoter. Use of this modified construct allowed to the establish a mutine transgenic line (TG). TG offspring were examined at 6, 12, and 24 weeks. All showed a significantly higher heart weight-to-body weight ratio. Northern blot analysis confirmed the expression of transgene in the heart, and enzyme-linked immunosorbent assay demonstrated the presence of TNF-alpha protein. The TG heart demonstrated a mild, diffuse, lymphohistiocytic interstitial inflammatory infiltrate. Cardiomyocyte necrosis and apoptosis were present but not abundant. Magnetic resonance imaging showed that the TG heart was significantly dilated with reduced ejection fraction. Although the left ventricular dP/dtmax was not different at baseline, its responsiveness to isoproterenol was significantly blunted in TG. Atrial natriuretic factor was expressed in the TG ventricle. A group of TG died spontaneously, and subsequent autopsies revealed exceptional dilation of the heart, increased lung weight, and pleural effusion, suggesting that they died of congestive heart failure. The cumulative mortality rate at 6 months was 23%. In conclusion, the mouse overexpressing TNF-alpha recapitulated the phenotype of congestive heart failure. This provides a novel model to elucidate the role of this cytokine in the development of congestive heart failure.

Carbon Monoxide Poisoning: Pathogenesis, Management, and Future Directions of Therapy

Carbon monoxide (CO) poisoning affects 50,000 people a year in the United States. The clinical presentation runs a spectrum, ranging from headache and dizziness to coma and death, with a mortality rate ranging from 1 to 3%. A significant number of patients who survive CO poisoning suffer from long-term neurological and affective sequelae. The neurologic deficits do not necessarily correlate with blood CO levels but likely result from the pleiotropic effects of CO on cellular mitochondrial respiration, cellular energy utilization, inflammation, and free radical generation, especially in the brain and heart. Long-term neurocognitive deficits occur in 15-40% of patients, whereas approximately one-third of moderate to severely poisoned patients exhibit cardiac dysfunction, including arrhythmia, left ventricular systolic dysfunction, and myocardial infarction. Imaging studies reveal cerebral white matter hyperintensities, with delayed posthypoxic leukoencephalopathy or diffuse brain atrophy. Management of these patients requires the identification of accompanying drug ingestions, especially in the setting of intentional poisoning, fire-related toxic gas exposures, and inhalational injuries. Conventional therapy is limited to normobaric and hyperbaric oxygen, with no available antidotal therapy. Although hyperbaric oxygen significantly reduces the permanent neurological and affective effects of CO poisoning, a portion of survivors still have substantial morbidity. There has been some early success in therapies targeting the downstream inflammatory and oxidative effects of CO poisoning. New methods to directly target the toxic effect of CO, such as CO scavenging agents, are currently under development.

The role of tumor necrosis factor in the pathophysiology of heart failure

Recent studies have focused their attention on the role of the proinflammatory cytokine tumor necrosis factor (TNF) in the development of heart failure. First recognized as an endotoxin-induced serum factor that caused necrosis of tumors and cachexia, it is now recognized that TNF participates in the pathophysiology of a group of inflammatory diseases including rheumatoid arthritis and Crohn's disease. The normal heart does not express TNF; however, the failing heart produces robust quantities. Furthermore, there is a direct relationship between the level of TNF expression and the severity of disease. In addition, both in vivo and in vitro studies demonstrate that TNF effects cellular and biochemical changes that mirror those seen in patients with congestive heart failure. Furthermore, in animal models, the development of the heart failure phenotype can be abrogated at least in part by anticytokine therapy. Based on information from experimental studies, investigators are now evaluating the clinical efficacy of novel anticytokine and anti-TNF strategies in patients with heart failure; one such strategy is the use of a recombinantly produced chimeric TNF alpha soluble receptor. Thus, in view of the emerging importance of proinflammatory cytokines in the pathogenesis of heart disease, we review the biology of TNF, its role in inflammatory diseases, the effects of TNF on the physiology of the heart and the development of clinical strategies that target the cytokine pathways.

Interplay of matrix metalloproteinases, tissue inhibitors of metalloproteinases and their regulators in cardiac matrix remodeling

Myocardial fibrosis due to maladaptive extracellular matrix remodeling contributes to dysfunction of the failing heart. Further elucidation of the mechanism by which myocardial fibrosis and dilatation can be prevented or even reversed remains of great interest as a potential means to limit myocardial remodeling and dysfunction. Matrix metalloproteinases (MMPs) are the driving force behind extracellular matrix degradation during remodeling and are increased in the failing human heart. MMPs are regulated by a variety of growth factors, cytokines, and matrix fragments such as matrikines. In the present report, we discuss the regulation of MMPs, the role of MMPs in the development of cardiac fibrosis, and the modulation of MMP activity using gene transfer and knockout technologies. We also present recent findings from our laboratory on the regulation of the extracellular MMP inducer (EMMPRIN), MMPs, and transforming growth factor-beta(1) in the failing human heart before and after left ventricular assist device support, as well as the possibility of preventing ventricular fibrosis using different anti-MMP strategies. Several studies suggest that such modulation of MMP activity can alter ventricular remodeling, myocardial dysfunction, and the progression of heart failure. It is therefore suggested that the interplay of MMPs and their regulators is important in the development of the heart failure phenotype, and myocardial fibrosis in heart failure may be modified by modulating MMP activity.

Myocardial extracellular matrix remodeling in transgenic mice overexpressing tumor necrosis factor alpha can be modulated by anti-tumor necrosis factor alpha therapy

Myocardial fibrosis caused by maladaptive extracellular matrix (ECM) remodeling is implicated in the dysfunction of the failing heart. Matrix metalloproteinases (MMPs) regulate ECM remodeling, and are regulated by cytokines. Transgenic mice with cardiac-specific overexpression of tumor necrosis factor alpha (TNF-alpha) (TNF1.6) develop heart failure. We hypothesized that modulation of TNF-alpha and/or MMP activity might alter the myocardial ECM remodeling process and the development of heart failure. To test this hypothesis, we took advantage of the TNF1.6 mice and studied soluble and total collagens and collagen type profiling by using hydroxyproline quantification, Sircol collagen assay, Northern blot analysis, and immunohistochemistry and studied myocardial function by using echocardiography. Progressive ventricular hypertrophy and dilation in the TNF1.6 mice were accompanied by a significant increase in MMP-2 and MMP-9 activity, an increase in collagen synthesis, deposition, and denaturation, and a decrease in undenatured collagens. In young TNF1.6 mice, these changes in the ECM were associated with marked diastolic dysfunction as demonstrated by significantly reduced transmitral Doppler echocardiographic E/A wave ratio. Anti-TNF-alpha treatment with adenoviral vector expressing soluble TNF-alpha receptor type I attenuated both MMP-2 and MMP-9 activity, prevented further collagen synthesis, deposition and denaturation, and preserved myocardial diastolic function in young, but not old, TNF1.6 mice. The results suggest a critical role of TNF-alpha and MMPs in myocardial matrix remodeling and functional regulation and support the hypothesis that both TNF-alpha and MMPs may serve as potential therapeutic targets in the treatment of heart failure.

Differential expression of tissue inhibitors of metalloproteinases in the failing human heart

BACKGROUND

Extracellular matrix turnover is regulated by matrix metalloproteinases (MMPs) and a family of tissue inhibitors of metalloproteinases (TIMPs). Together, these proteins may contribute to myocardial remodeling in congestive heart failure. We hypothesized that the expression of MMPs and TIMPs might be differentially regulated in the failing human heart.

METHODS AND RESULTS

Northern blot analyses were performed with probes to TIMP-1 to -4 and GAPDH with poly A+ mRNA from ventricular tissues of patients with ischemic cardiomyopathy (ICM, n=16) or idiopathic dilated cardiomyopathy (DCM, n=15) and nonfailing control hearts (n=15). TIMP-1 to -4 and MMP-9 proteins were quantified by ELISA and/or Western blot, and the total gelatinolytic activity was studied by gelatin zymography. The results showed that cardiac expression of TIMP-1 and -3 transcripts and proteins was significantly reduced in ICM and DCM. No significant difference was observed in TIMP-2 and -4 transcripts. However, TIMP-4 protein was significantly reduced in ICM myocardium. MMP-9 protein content and total gelatinolytic activity were upregulated in the same samples.

CONCLUSIONS

These studies demonstrated a selective downregulation of TIMPs along with upregulation of MMP-9 and gelatinolytic activity in the failing hearts, alterations that favor matrix degradation and turnover. These findings might be of pathophysiological significance and might suggest new therapeutic targets for limiting the ventricular remodeling and dilatation process characteristic of the failing human heart.

Downregulation of matrix metalloproteinases and reduction in collagen damage in the failing human heart after support with left ventricular assist devices

BACKGROUND

Left ventricular assist device (LVAD) support of the failing heart induces salutary changes in myocardial structure and function. Matrix metalloproteinases (MMPs) are increased in the failing heart and are induced by stretch in cardiac cells in vitro. We hypothesized that mechanical unloading may affect LV plasticity by regulating MMPs and their substrates.

METHODS AND RESULTS

LV samples were collected from patients with dilated cardiomyopathy (DCM, n=14) or ischemic cardiomyopathy (ICM, n=16) at the time of implantation of the LVAD and again during cardiac transplantation. MMP-1, -3, and -9 were measured by ELISA, MMP-2 and -9 gelatinolytic activity by gelatin zymography, and tissue inhibitors of metalloproteinases (TIMPs) by Western blot. Total soluble and insoluble collagens were separated by pepsin solubilization, and the contents were determined by quantification of hydroxyproline. The undenatured soluble collagen was measured by Sircol collagen assay. The results showed that MMP-1 and -9 were decreased, whereas TIMP-1 and -3 were increased, but there was no change in MMP-2 and -3 and TIMP-2 and -4 after LVAD support. The undenatured collagen was increased, with the ratio of undenatured to total soluble collagens increased in ICM and that of insoluble to total soluble collagens increased in DCM after LVAD support.

CONCLUSIONS

The reduced MMPs and increased TIMPs and ratios of undenatured to total soluble collagens and insoluble to total soluble collagens after LVAD support suggest that reduced MMP activity diminished damage to the matrix. These changes may contribute to the functional recovery and LV plasticity after LVAD support.

Ultrasound-targeted microbubble destruction to deliver siRNA cancer therapy

Microbubble contrast agents can specifically deliver nucleic acids to target tissues when exposed to ultrasound treatment parameters that mediate microbubble destruction. In this study, we evaluated whether microbubbles and ultrasound-targeted microbubble destruction (UTMD) could be used to enhance delivery of EGF receptor (EGFR)-directed siRNA to murine squamous cell carcinomas. Custom-designed microbubbles efficiently bound siRNA and mediated RNAse protection. UTMD-mediated delivery of microbubbles loaded with EGFR-directed siRNA to murine squamous carcinoma cells in vitro reduced EGFR expression and EGF-dependent growth, relative to delivery of control siRNA. Similarly, serial UTMD-mediated delivery of EGFR siRNA to squamous cell carcinoma in vivo decreased EGFR expression and increased tumor doubling time, relative to controls receiving EGFR siRNA-loaded microbubbles but not ultrasound or control siRNA-loaded microbubbles and UTMD. Taken together, our results offer a preclinical proof-of-concept for customized microbubbles and UTMD to deliver gene-targeted siRNA for cancer therapy.

Atrial contractile dysfunction, fibrosis, and arrhythmias in a mouse model of cardiomyopathy secondary to cardiac-specific overexpression of tumor necrosis factor-{alpha}

Transgenic mice overexpressing the inflammatory cytokine TNF-alpha in the heart develop a progressive heart failure syndrome characterized by biventricular dilatation, decreased ejection fraction, decreased survival compared with non-transgenic littermates, and earlier pathology in males. TNF-alpha mice (TNF1.6) develop atrial arrhythmias on ambulatory telemetry monitoring that worsen with age and are more severe in males. We performed in vivo electrophysiological testing in transgenic and control mice, ex vivo optical mapping of voltage in the atria of isolated perfused TNF1.6 hearts, and in vitro studies on isolated atrial muscle and cells to study the mechanisms that lead to the spontaneous arrhythmias. Programmed stimulation induces atrial arrhythmias (n = 8/32) in TNF1.6 but not in control mice (n = 0/37), with a higher inducibility in males. In the isolated perfused hearts, programmed stimulation with single extra beats elicits reentrant atrial arrhythmias (n = 6/6) in TNF1.6 but not control hearts due to slow heterogeneous conduction of the premature beats. Lowering extracellular Ca(2+) normalizes conduction and prevents the arrhythmias. Atrial muscle and cells from TNF1.6 compared with control mice exhibit increased collagen deposition, decreased contractile function, and abnormal systolic and diastolic Ca(2+) handling. Thus abnormalities in action potential propagation and Ca(2+) handling contribute to the initiation of atrial arrhythmias in this mouse model of heart failure.

Tumor necrosis factor receptors 1 and 2 differentially regulate survival, cardiac dysfunction, and remodeling in transgenic mice with tumor necrosis factor-alpha-induced cardiomyopathy

BACKGROUND

Tumor necrosis factor (TNF)-alpha plays a pathophysiological role in heart failure. Although both TNF receptor 1 (TNFR1) and 2 (TNFR2) are present in the heart, comparatively little is known about the role of TNFR2.

METHODS AND RESULTS

We bred TNFR1-knockout (KO) or TNFR2KO mice to transgenic (TG) mice with cardiac-specific overexpression of TNF-alpha and analyzed resultant progeny. Six groups of male and female mice were studied: wild type (WT) with wild receptors (WT/W), TG with wild receptors (TG/W), TG with heterozygous receptor KO (TG/R1+/- or TG/R2+/-), and TG with homozygous receptor KO (TG/R1-/- or TG/R2-/-). Both male and female TG mice displayed cardiac hypertrophy, dilation, and reduced cardiac function. Male TG mice were more severely affected than genotypically matched females and died of heart failure at a younger age. Survival, cardiac function, and remodeling of TG/R1+/- and TG/R1-/- mice were improved relative to TG/W mice in both males and females. However, the survival of female TG/R2+/- and TG/R2-/- mice was worse than that of TG/W mice, with increased left ventricular dimension and left ventricular weight/body weight ratios. The cardiac TNF-alpha protein level was upregulated in TG/R1-/- and TG/R2-/- compared with TG/W mice, whereas the level of TNF receptors was not downregulated in TG/W relative to WT/W mice.

CONCLUSIONS

Ablation of the TNFR2 gene exacerbates heart failure and reduces survival, whereas ablation of TNFR1 blunts heart failure and improves survival. Signaling via TNFR2 may play a cardioprotective role in the pathogenesis of cytokine-mediated heart failure.

Proinflammatory cytokines regulate tissue inhibitors of metalloproteinases and disintegrin metalloproteinase in cardiac cells

OBJECTIVE

Tissue inhibitors of metalloproteinases (TIMPs) are downregulated in the failing human heart. The objective of the present study was to test the hypothesis that cytokines might be involved in the regulation of TIMPs in cardiac cells.

METHODS

Neonatal Sprague-Dawley rat ventricular cells were exposed to 100 units/ml tumor necrosis factor-alpha and/or 5 ng/ml interleukin-1 beta. The mRNA and protein expression of TIMPs-1-4 and disintegrin metalloproteinase was analyzed using Northern blot, ELISA and/or Western blot, respectively. Proteolytic activity and extracellular matrix degradation and turnover were determined using gelatin zymography and pulse-chase experiments.

RESULTS

The TIMP-1 mRNA was upregulated in cardiac cells, while TIMP-1 protein levels were unchanged in myocytes but downregulated in non-myocytes. The TIMP-2 expression did not change with the cytokine treatment. TIMP-3 was downregulated at both the mRNA and protein levels in cardiac cells. TIMP-4 protein was transiently increased and then returned to control level. In contrast, disintegrin metalloproteinase mRNA and protein were significantly upregulated in those cells. The gelatinolytic activity and extracellular matrix protein degradation were significantly increased.

CONCLUSIONS

Tumor necrosis factor-alpha and interleukin-1 beta regulate the expression of TIMPs and disintegrin metalloproteinase, which may in turn contribute to the increased matrix degradation in cardiac cells. Since heart failure in humans is characterized by both re-expression of myocardial cytokines and remodeling of the extracellular matrix, those in vitro results suggest a potential role for those cytokines in the regulation of extracellular matrix remodeling and therefore in the transition to the end-stage heart failure phenotype.

Cardiac-specific overexpression of tumor necrosis factor-alpha causes lethal myocarditis in transgenic mice

BACKGROUND

Tumor necrosis factor (TNF)-alpha, a proinflammatory cytokine with negative inotropic effects, can be detected in myocardium with end-stage heart failure, after endotoxin administration, and during transplant rejection. Various studies suggest that TNF-alpha participates in the pathogenesis of cardiac dysfunction. To test this hypothesis, transgenic mice were made that selectively overexpress TNF-alpha in cardiomyocytes.

METHODS AND RESULTS

A transgene construct was made containing the murine alpha-myosin heavy chain promoter and the coding sequence of murine TNF-alpha, followed by the simian virus 40 T-antigen intron and polyadenylation signals. Injection of this construct into fertilized eggs yielded three transgenic mice, all of which died spontaneously before the completion of weaning. Gross pathologic analysis of these mice demonstrated a decrease in body weight with markedly increased heart weight. Histologic examination of the heart revealed a substantial, diffuse lymphohistiocytic inflammatory infiltrate, associated with interstitial edema. Reverse transcriptase polymerase chain reaction showed that the transgene was expressed in the heart. Enzyme-linked immunosorbent assay demonstrated a substantial amount of TNF-alpha protein in the transgenic heart.

CONCLUSION

Overexpression of TNF-alpha in the heart leads to severe myocarditis and cardiomegaly. These results support the hypothesis that myocardial expression of TNF-alpha can contribute to the pathogenesis of cardiac dysfunction.

Expression of proinflammatory cytokines in the failing human heart: comparison of recent-onset and end-stage congestive heart failure

BACKGROUND

Plasma levels of proinflammatory cytokines, including tumor necrosis factor (TNF)-alpha and interleukin (IL)-6, are elevated in patients with congestive heart failure (CHF). Recent studies suggest that the failing human heart is a source of proinflammatory cytokines in the end-stage failing heart. However, the relevance of plasma levels to those of the myocardium remains undefined. We sought to compare cytokine expression in early and end-stage CHF, and to evaluate the correlation of tissue expression to plasma levels.

METHODS

Two patient populations were studied: patients with recent-onset CHF, all with symptoms less than 6 months (n = 17, duration of symptoms 2.1 +/- 1.6 months, range of New York Heart Association (NYHA) 1 to 3), and end-stage heart-failure patients (n = 7) who underwent left-ventricular assist-device (LVAD) implantation (Duration of symptoms 47.1 +/- 28.0 months, all NYHA class 4). Plasma levels of TNF-alpha and IL-6 proteins were evaluated by an Enzyme-Linked Immuno-Sorbent Assay (ELISA), while myocardial levels of cytokine transcripts were assessed by ribonuclease (Rnase) protection assay.

RESULTS

In patients with end-stage heart failure, TNF-alpha and IL-6 were increased in the plasma as well as in the myocardium (plasma: TNF-alpha = 7.7 +/- 2.3 pg/ml, IL-6 = 45.0 +/- 47.1 pg/ml; myocardium: TNF-alpha = 0.31 +/- 0.15% of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) expression, IL-6 = 1.56 +/- 1.54% ). In contrast, despite elevated plasma levels of TNF-alpha and IL-6, the myocardium of patients with the recent onset of symptoms demonstrated minimal expression of TNF-alpha and IL-6 messenger ribonucleic acid (mRNA) (plasma: TNF-alpha = 4.3 +/- 1.7 pg/ml, IL-6 = 3.3 +/- 1.8 pg/ml; myocardium: TNF-alpha = 0.13 +/- 0. 04%, IL-6 = 0.02 +/- 0.04%). Plasma levels of TNF-alpha were significantly correlated with those in the myocardium when both populations were combined. (r = 0.69, p < 0.001).

CONCLUSIONS

Cytokines are expressed in the myocardium in end-stage heart failure to a much greater degree than in patients with the recent-onset of symptoms. This suggests that induction of cytokines in the myocardium is a relatively late event in the pathogenesis of CHF. Furthermore, plasma levels of TNF-alpha correlates with mRNA expression in the myocardium and thus may serve as an appropriate marker of myocardial cytokine activation. Whether the production of cytokines in the failing human heart precedes the elevation of cytokines in the plasma remains undefined. Therefore, we studied expression of TNF-alpha and IL-6 in the myocardium as well as in the plasma in patients with early and end-stage CHF. The results have demonstrated that cytokines are expressed in the myocardium in end-stage heart failure to a much greater degree than in patients with the recent onset of symptoms. This suggests that induction of cytokines in the myocardium is a relatively late event in the pathogenesis of CHF.

Soluble tumor necrosis factor receptor abrogates myocardial inflammation but not hypertrophy in cytokine-induced cardiomyopathy

BACKGROUND

Transgenic mice with cardiac-specific overexpression of tumor necrosis factor (TNF)-alpha develop dilated cardiomyopathy. The present study was designed to evaluate therapeutic effects of adenovirus-mediated neutralization of TNF-alpha on this model.

METHODS AND RESULTS

An adenovirus encoding the 55-kDa TNF receptor-IgG fusion protein (AdTNFRI) was injected intravenously into 6-week-old transgenic mice, which resulted in high levels of TNFRI in both plasma and myocardium. AdTNFRI did not reverse cardiomegaly but abrogated myocardial inflammation. Furthermore, AdTNFRI blocked the myocardial expression of intercellular adhesion molecule-1 and downstream cytokines, including interleukin-1beta and monocyte chemotactic protein-1. Downregulation of alpha-myosin heavy chain was restored by the treatment, whereas upregulation of beta-myosin heavy chain was not reversed. In contrast, the downregulation of sarcoplasmic reticulum Ca(2+)-ATPase and phospholamban was normalized by AdTNFRI. Echocardiographic measurements showed that left ventricular end-systolic diameter was significantly larger in transgenic mice than in control mice, and this increase was reversed by the AdTNFRI treatment. However, left ventricular wall thickening was not reversed.

CONCLUSIONS

These results suggest that anti-TNF therapy may hold promise in the treatment of end-stage heart failure.

Calcium-dependent arrhythmias in transgenic mice with heart failure

Transgenic mice overexpressing the inflammatory cytokine tumor necrosis factor (TNF)-alpha (TNF-alpha mice) in the heart develop a progressive heart failure syndrome characterized by biventricular dilatation, decreased ejection fraction, atrial and ventricular arrhythmias on ambulatory telemetry monitoring, and decreased survival compared with nontransgenic littermates. Programmed stimulation in vitro with single extra beats elicits reentrant ventricular arrhythmias in TNF-alpha (n = 12 of 13 hearts) but not in control hearts. We performed optical mapping of voltage and Ca(2+) in isolated perfused ventricles of TNF-alpha mice to study the mechanisms that lead to the initiation and maintenance of the arrhythmias. When compared with controls, hearts from TNF-alpha mice have prolonged of action potential durations (action potential duration at 90% repolarization: 23 +/- 2 ms, n = 7, vs. 18 +/- 1 ms, n = 5; P < 0.05), no increased dispersion of refractoriness between apex and base, elevated diastolic and depressed systolic [Ca(2+)], and prolonged Ca(2+) transients (72 +/- 6 ms, n = 10, vs. 54 +/- 5 ms, n = 8; P < 0.01). Premature beats have diminished action potential amplitudes and conduct in a slow, heterogeneous manner. Lowering extracellular [Ca(2+)] normalizes conduction and prevents inducible arrhythmias. Thus both action potential prolongation and abnormal Ca(2+) handling may contribute to the initiation of reentrant arrhythmias in this heart failure model by mechanisms distinct from enhanced dispersion of refractoriness or triggered activity.

Sex-related survival differences in murine cardiomyopathy are associated with differences in TNF-receptor expression

Epidemiological evidence suggests that the prognosis of heart failure in women is better than in men. In our murine model of dilated cardiomyopathy arising from cardiac-specific overexpression of TNF-alpha, the 6-month survival rate was significantly better in females than in males. Young female transgenic mice exhibited left ventricular wall thickening without dilatation, whereas age-matched male transgenic hearts were markedly dilated. Basal and isoproterenol-stimulated fractional shortening was preserved in female transgenic mice, but not in male transgenic mice. Myocardial expression of proinflammatory cytokines and the extent of myocardial infiltrates were similar in male and female transgenic mice. Myocardial expression of TNF-receptor mRNAs (type I and type II) was significantly higher in male mice in both transgenic and wild-type littermates, whereas sex-specific differences were not observed in either peripheral white blood cells or liver tissue. After TNF-alpha challenge, myocardial but not liver production of ceramide was significantly higher in male than in female mice. Thus, differential expression of myocardial TNF receptors may contribute to sex differences in the severity of congestive heart failure and mortality consequent to cardiac-specific overexpression of TNF-alpha.

Relaxin suppresses atrial fibrillation by reversing fibrosis and myocyte hypertrophy and increasing conduction velocity and sodium current in spontaneously hypertensive rat hearts

RATIONALE

Atrial fibrillation (AF) contributes significantly to morbidity and mortality in elderly and hypertensive patients and has been correlated to enhanced atrial fibrosis. Despite a lack of direct evidence that fibrosis causes AF, reversal of fibrosis is considered a plausible therapy.

OBJECTIVE

To evaluate the efficacy of the antifibrotic hormone relaxin (RLX) in suppressing AF in spontaneously hypertensive rats (SHR).

METHODS AND RESULTS

Normotensive Wistar-Kyoto (WKY) and SHR were treated for 2 weeks with vehicle (WKY+V and SHR+V) or RLX (0.4 mg/kg per day, SHR+RLX) using implantable mini-pumps. Hearts were perfused, mapped optically to analyze action potential durations, intracellular Ca²⁺ transients, and restitution kinetics, and tested for AF vulnerability. SHR hearts had slower conduction velocity (CV; P<0.01 versus WKY), steeper CV restitution kinetics, greater collagen deposition, higher levels of transcripts for transforming growth factor-β, metalloproteinase-2, metalloproteinase-9, collagen I/III, and reduced connexin 43 phosphorylation (P<0.05 versus WKY). Programmed stimulation triggered sustained AF in SHR (n=5/5) and SHR+V (n=4/4), but not in WKY (n=0/5) and SHR+RLX (n=1/8; P<0.01). RLX treatment reversed the transcripts for fibrosis, flattened CV restitution kinetics, reduced action potential duration at 90% recovery to baseline, increased CV (P<0.01), and reversed atrial hypertrophy (P<0.05). Independent of antifibrotic actions, RLX (0.1 µmol/L) increased Na⁺ current density, INa (≈2-fold in 48 hours) in human cardiomyocytes derived from inducible pluripotent stem cells (n=18/18; P<0.01).

CONCLUSIONS

RLX treatment suppressed AF in SHR hearts by increasing CV from a combination of reversal of fibrosis and hypertrophy and by increasing INa. The study provides compelling evidence that RLX may provide a novel therapy to manage AF in humans by reversing fibrosis and hypertrophy and by modulating cardiac ionic currents.

Adenosine inhibits lipopolysaccharide-induced cardiac expression of tumor necrosis factor-alpha

Tumor necrosis factor-alpha (TNF-alpha) is elevated in the failing heart. Very little is known about regulation of TNF-alpha in cardiomyocytes. TNF-alpha expression by macrophages is diminished by adenosine. Therefore, we hypothesized that a similar mechanism might occur in the heart. Neonatal rat myocytes were stimulated with lipopolysaccharide (LPS), and TNF-alpha was measured by ELISA. In the absence of LPS, myocytes did not release TNF-alpha in the medium. After exposure to LPS, TNF-alpha increased to 70.1+/-3.5 pg/mL at 6 hours. Immunofluorescent staining confirmed that TNF-alpha was expressed in myocytes. Adenosine decreased TNF-alpha in a dose-dependent manner (1 to 100 micromol/L, 37% to 65% decrease, P<.01). Adenosine also decreased TNF-alpha in cell homogenates by 78% (P<.0001). The effect of adenosine could be replicated by the A2 agonist PD-125944 (DPMA), by cAMP agonists 8-bromo-cAMP, forskolin, and Ro 20-1724, but not by A1 and A3 agonists. Conversely, the effect of adenosine could be suppressed by the adenylate cyclase inhibitor MDL-12,330. Adenosine also inhibited TNF-alpha in adult rat ventricular myocytes (-60%, P<.005) and rat papillary muscles (-55%, P<.05). In neonatal myocytes, adenosine normalized LPS-induced calcium changes and improved LPS-induced negative inotropic (P<.01) and negative lusitropic (P<.01) effects. Our results demonstrate that adenosine can significantly diminish TNF-alpha levels in the heart. The effect appears to be mediated by the A2 receptor and transduced through a G protein-adenylyl cyclase pathway. These results may explain some cardioprotective effects of adenosine and provide a novel pharmacological intervention in congestive heart failure.

Electrical remodeling of cardiac myocytes from mice with heart failure due to the overexpression of tumor necrosis factor-alpha

Mice that overexpress the inflammatory cytokine tumor necrosis factor-alpha in the heart (TNF mice) develop heart failure characterized by atrial and ventricular dilatation, decreased ejection fraction, atrial and ventricular arrhythmias, and increased mortality (males > females). Abnormalities in Ca2+ handling, prolonged action potential duration (APD), calcium alternans, and reentrant atrial and ventricular arrhythmias were previously observed with the use of optical mapping of perfused hearts from TNF mice. We therefore tested whether altered voltage-gated outward K+ and/or inward Ca2+ currents contribute to the altered action potential characteristics and the increased vulnerability to arrhythmias. Whole cell voltage-clamp recordings of K+ currents from left ventricular myocytes of TNF mice revealed an approximately 50% decrease in the rapidly activating, rapidly inactivating transient outward K+ current Ito and in the rapidly activating, slowly inactivating delayed rectifier current IK,slow1, an approximately 25% decrease in the rapidly activating, slowly inactivating delayed rectifier current IK,slow2, and no significant change in the steady-state current Iss compared with controls. Peak amplitudes and inactivation kinetics of the L-type Ca2+ current ICa,L were not altered. Western blot analyses revealed a reduction in the proteins underlying Kv4.2, Kv4.3, and Kv1.5. Thus decreased K+ channel expression is largely responsible for the prolonged APD in the TNF mice and may, along with abnormalities in Ca2+ handling, contribute to arrhythmias.

Overexpression of tumor necrosis factor- alpha activates both anti- and pro-apoptotic pathways in the myocardium

We have previously reported that mice with cardiac-specific overexpression of tumor necrosis factor (TNF)- alpha develop myocardial inflammation, cardiac hypertrophy, and dilated cardiomyopathy. TNF- alpha is reported to induce apoptosis in cultured cardiac myocytes. To investigate the role of apoptosis in this transgenic model, wild-type controls (WT) and transgenic mice (TG) at the age of 1, 8, and 40 weeks were analyzed. Increased incidence of apoptosis in TG was indicated by DNA laddering. TUNEL assays revealed that the frequencies of apoptotic cells were increased in the TG myocardium at all ages. However, as revealed by histochemical and immunofluorescent methods, most of the apoptotic cells appeared to be non-myocytes even in the mice with overt congestive heart failure. To elucidate the signaling pathways responsible for TNF- alpha induced apoptosis, expression of apoptosis-related genes were evaluated by multi-probe RNase protection assays. Transcripts for death-domain-related proteins, including TNFR1, Fas, FADD, TRADD, and RIP, were constitutively expressed in WT and upregulated in the TG myocardium. Expression of caspase-1 through -8 was also enhanced in TG. While both anti- and pro-apoptotic Bcl-2 family genes were constitutively expressed in WT, TNF- alpha overexpression strongly induced anti-apoptotic A1 in the myocardium. Furthermore, TNF- alpha overexpression activated NF- kappa B, a mediator of anti-apoptotic pathways, in the myocardium. Thus, overexpression of TNF- alpha activated both anti- and pro-apoptotic pathways in the myocardium, resulting in an increase of apoptosis, primarily in non-myocytes. These results suggest that TNF- alpha by itself is not sufficient to induce apoptosis in cardiac myocytes in vivo.

Sustained Whole-Body Functional Rescue in Congestive Heart Failure and Muscular Dystrophy Hamsters by Systemic Gene Transfer

BACKGROUND

The success of muscular dystrophy gene therapy requires widespread and stable gene delivery with minimal invasiveness. Here, we investigated the therapeutic effect of systemic delivery of adeno-associated virus (AAV) vectors carrying human delta-sarcoglycan (delta-SG) gene in TO-2 hamsters, a congestive heart failure and muscular dystrophy model with a delta-SG gene mutation.

METHODS AND RESULTS

A single injection of double-stranded AAV serotype 8 vector carrying human delta-SG gene without the need of any physical or pharmaceutical interventions achieved nearly complete gene transfer and tissue-specific expression in the heart and skeletal muscles of the diseased hamsters. Broad and sustained (>12 months) restoration of the missing delta-SG gene in the TO-2 hamsters corrected muscle cell membrane leakiness throughout the body and normalized serum creatine kinase levels (a 50- to 100-fold drop). Histological examination revealed minimal or the absence of central nucleation, fibrosis, and calcification in the skeletal muscle and heart. Whole-body functional analysis such as treadmill running showed dramatic improvement, similar to the wild-type F1B hamsters. Furthermore, cardiac functional studies with echocardiography revealed significantly increased percent fractional shortening and decreased left ventricular end-diastolic and end-systolic dimensions in the treated TO-2 hamsters. The survival time of the animals was also dramatically extended.

CONCLUSIONS

Systemic gene transfer of delta-SG by the AAV serotype 8 vector could effectively ameliorate cardiac and skeletal muscle pathology, profoundly improve cardiac and whole-body functions, and significantly prolong the lifespan of the treated TO-2 hamsters.

Cardiac-specific leptin receptor deletion exacerbates ischaemic heart failure in mice

AIMS

the obesity-related adipokine, leptin, has multiple actions on peripheral organs, including the mitigation of adverse cardiovascular outcomes after myocardial infarction (MI). Although we recently demonstrated that leptin, its receptor, and downstream signalling are up-regulated in the heart after MI, the significance of intact cardiomyoctye leptin signalling is unknown. Therefore, our objective was to generate a cardiomyocyte-specific leptin receptor knock-out (ObRKO) mouse to determine whether worse cardiac outcomes after MI result from impaired leptin signalling in cardiomyocytes.

METHODS AND RESULTS

tamoxifen-inducible ObRKO mice were subjected to experimental MI or sham surgeries and studied after 1 month. After MI, ObRKO mice displayed a loss of cardiac signal transducer and activator of transcription (STAT) 3 and adenosine monophosphate-activated protein kinase (AMPK) signalling. Worse survival and cardiac morbidity were also seen in the ObRKO mouse post-MI, including decreased contractile function and glycolytic metabolism, and increased left ventricular dilation, hypertrophy, collagen deposition, matrix metalloproteinase activity, apoptosis, and inflammation. Treatment of ObRKO mice post-MI with an ObR-independent AMPK activator improved cardiac function and restored many of these maladaptive processes to wild-type levels.

CONCLUSION

these data indicate that leptin signalling mitigates cardiac injury in the post-MI failing heart by acting directly on cardiomyocytes to increase STAT3 and AMPK activation, to decrease cardiac hypertrophy, apoptosis, and inflammation, and to limit deleterious changes in cardiac structure, function, and glycolytic metabolism.

Brain cDNA clone for human cholinesterase

A cDNA library from human basal ganglia was screened with oligonucleotide probes corresponding to portions of the amino acid sequence of human serum cholinesterase (EC 3.1.1.8). Five overlapping clones, representing 2.4 kilobases, were isolated. The sequenced cDNA contained 207 base pairs of coding sequence 5' to the amino terminus of the mature protein in which there were four ATG translation start sites in the same reading frame as the protein. Only the ATG coding for Met-(-28) lay within a favorable consensus sequence for functional initiators. There were 1722 base pairs of coding sequence corresponding to the protein found circulating in human serum. The amino acid sequence deduced from the cDNA exactly matched the 574 amino acid sequence of human serum cholinesterase, as previously determined by Edman degradation. Therefore, our clones represented cholinesterase (EC 3.1.1.8) rather than acetylcholinesterase (EC 3.1.1.7). It was concluded that the amino acid sequences of cholinesterase from two different tissues, human brain and human serum, were identical. Hybridization of genomic DNA blots suggested that a single gene, or very few genes, coded for cholinesterase.

Effects of tumor necrosis factor gene polymorphisms on patients with congestive heart failure. VEST Investigators for TNF Genotype Analysis. Vesnarinone Survival Trial

BACKGROUND

Tumor necrosis factor-alpha (TNF-alpha) is known to be elevated in patients with congestive heart failure (CHF). Two biallelic polymorphisms have been identified in the TNF gene locus: one in the promoter region of TNF-alpha (TNFA1/2), and the other in the first intron of TNF-beta (TNFB1/2). Both TNFA2 and TNFB2 alleles are associated with high TNF-alpha production in vitro and susceptibility to inflammatory diseases. Given the importance of TNF-alpha in the pathogenesis of CHF, we studied the prevalence of TNF gene polymorphisms in CHF patients and the correlation of genotypes to in vivo TNF-alpha levels.

METHODS AND RESULTS

TNFA and TNFB genotypes were determined by the polymerase chain reaction-restriction fragment length polymorphism technique. There were no differences in the TNF allele frequencies between CHF (n=229; TNFA1/2=0.84/0.16, TNFB1/2=0.33/0.67) and control subjects (n=139; TNFA1/2=0.84/0.16, TNFB1/2=0.32/0.68). In 211 patients with CHF, circulating levels of TNF-alpha and the soluble receptors type I and type II were measured by ELISA: 6.18+/-3.59 pg/mL, 1768+/-761 pg/mL, and 4484+/-1750 pg/mL, respectively. There were no correlations between TNFA or TNFB genotypes and circulating levels of TNF-alpha or its soluble receptors in the CHF patients.

CONCLUSIONS

Despite their association with other inflammatory diseases, neither TNFA nor TNFB polymorphisms are related to the presence of CHF or the elevation of circulating TNF-alpha. Thus, other factors may be more important in determining the circulating levels of TNF-alpha in CHF.

Anti-tumor necrosis factor-alpha antibody limits heart failure in a transgenic model

BACKGROUND

- Tumor necrosis factor (TNF)-alpha has been implicated in the pathophysiology of congestive heart failure. A strain of transgenic mice (TNF1.6) with cardiac-specific overexpression of TNF-alpha develop congestive heart failure.

METHODS AND RESULTS

To determine the effect of anti-TNF-alpha therapy in this model, we studied 3 groups: TNF1.6 mice treated with saline, wild-type mice treated with saline, and TNF1.6 mice treated with TNF-alpha neutralizing antibody (cV1q) from 6 to 12 weeks of age. We used echocardiography to compare cardiac hypertrophy, function, and catecholamine response at 12 weeks of age versus baseline (6 weeks). cV1q treatment did not limit cardiac hypertrophy, but it significantly improved basal fractional shortening and responsiveness to beta-adrenergic stimulation, and it limited development of cardiac dilation.

CONCLUSIONS

Blockade of TNF-alpha bioactivity by antibody therapy may both preserve cardiac function and partially reverse pathological changes in congestive heart failure.